1. Field of the Invention
The present invention relates to an audio circuit, especially to microphone detection and selection circuits and the related methods.
2. Description of Related Art
In order to satisfy the demand of identifying or recording acoustic signals, an electronic device usually has a built-in microphone and concurrently supports an external microphone which may electrically connect to the electronic device through a physical connection. If the electronic device detects no external microphones, it will carry out an audio process according to the acoustic signals from the built-in microphone; however, if the electronic device detects an external microphone, it will carry out the audio process with the external microphone instead. Generally, the electronic device will determine whether the external microphone exists by the jack detection with a microphone dedicated socket. But in some circumstances, the external microphone is integrated into an external device; under such conditions, the electronic device provided with proper design can also detect whether the external microphone of the external device exists through the jack detection with a composite socket. For instance, distinct positions of the composite socket of the electronic device are dedicated to connecting with distinct parts of the plug of the external device while the distinct parts are isolated from each other, and thus the electronic device can detect the signals corresponding to the distinct parts to catch the functions of the external device and find out whether the external device includes an external microphone. Unfortunately, the current art such as the disclosure of U.S. Pat. No. 7,912,501 uses an independent analog circuit to detect the existence of the external microphone through the composite socket; since the independent analog circuit consumes circuit area, leads to higher cost and is not integrated into the digital domain, it leaves room for improvement.
Besides, in the current art, once the electronic device detects the external microphone, it will use the external microphone instead to proceed with the audio process. However, if the electronic device is performing recording by the built-in microphone in the meantime, using the external microphone instead will most likely cause the discontinuous recording effect or lose a part of the recording content.
In consideration the deficits of the current microphone detection and selection technique, this industrial filed needs a device and a method to do microphone detection and/or choose an external microphone or a built-in microphone by the state of an electronic device.